Prior to Anglo settlement, the plentiful native grasses of the ponderosa pine forests of the American Southwest nourished herds of deer, antelope, bighorn sheep and elk as they moved between water sources. Domestic cattle and sheep were brought to the region by the Spanish in the late 1500s, but especially in the Arizona territories Apache raiding kept numbers relatively low. With the defeat of the Apaches by the U.S. Army in the 1870s and the arrival of the railroad in the late 1880s, livestock began to graze the forests by the tens of thousands.
By 1876, particularly in the northern areas populated by Navajos and Mormons, sheep, which would eat fragile pine saplings, outnumbered cattle 10 to 1. As drought plagued ranching operations to the east, especially in Texas, cattle gradually began to outnumber the sheep.
By the time federal forest reserves were created in the 1890s, ranchers and herders had become accustomed to unregulated use of public lands as range for their livestock. They rejected attempts by the foresters to put restrictions on their activities, arguing that they were helping to prevent fires from spreading through the forests by reducing grass cover.
By the turn of the century, after less than a generation of use by Euro-Americans, once rich grasslands were seriously degraded, and forest regeneration had ground to a halt. The forest floor in some places was "as bare and compact as a roadbed" (Baker et al. 1988).
There has been considerable debate over whether fire suppression or grazing has contributed more to the emergence of the dog-hair thickets that dominate today's forests. Studies have shown that even with the complete exclusion of fire, dense thickets will not develop if the grass remains ungrazed. In Zion National Park, a grazed study site with the same fire suppression history developed typical thickets. Furthermore, exclosure studies have shown that livestock alter ecosystem processes by reducing the cover of herbaceous plants and litter, disturbing and compacting soils, reducing water infiltration rates, and increasing soil erosion.
Cattle and to a lesser extent sheep still routinely graze the ponderosa forests of the region. The increase in density of tree cover has reduced both production and utilization of the resource, and total grazeable area has declined during the past half-century. It is argued by some that since the structure and composition of western forests have already been so altered, at this point removing cattle won’t do any good. However, there is good research showing that when cattle are removed from even quite dense forests, fire gradually returns to the system and thins the trees.
Arnold, J.F. 1950. Changes in ponderosa pine bunchgrass ranges in northern Arizona resulting from pine regeneration and grazing. Journal of Forestry 48:118-126. An early discussion of the contribution of livestock grazing to increases in the distribution and density of many woody species across the western United States.
Ashworth, Donna. 1991. Biography of a Small Mountain. Flagstaff, AZ: Small Mountain Books. The story of the early days of the timber industry and forest research in and around Flagstaff, Arizona.
Baker, Robert D.; Maxwell, R.S.; Treat, V.H.; Dethloff, H.C. 1988. Timeless heritage: a history of the Forest Service in the Southwest. FS–409. Washington, DC: U.S. Department of Agriculture, Forest Service. 208 p.
Belsky, A. J., and D. M. Blumenthal. 1997. Effects of live-stock grazing on stand dynamics and soils in upland forests of the Interior West. Conservation Biology 11:315327. This research review argues that livestock grazing is as important a factor in the decline of "forest health" as fire suppression of low-intensity fires and the selective logging of larger trees.
Cooper, Charles F. 1960. Changes in vegetation, structure, and growth of southwestern pine forests since white settlement. Ecological Monographs 30(2): 129-164. Classic study of southwestern forest ecosystem changes due to grazing, logging, and fire exclusion associated with European settlement.
Fleischner, Thomas L. 1994. Ecological Costs of Livestock Grazing in Western North America. Conservation Biology 8(3): 629-644. A comprehensive review of the impacts of grazing by a leading conservation biologist.
Fulé, P.Z., and W.W. Covington. 1997. Fire regimes and forest structure in the Sierra Madre Occidental, Durango, Mexico. Acta Botanica Mexicana 41:43-79. Fire exclusion coincided with heavy livestock grazing in the mid-twentieth century (1945-1955), except for a rare unharvested, frequently burned site.
Leopold, A. 1924. Grass, brush, timber and fire in southern AZ. Journal of Forestry 22:1-10. Pioneering observations about grazing, fire, and trees by the founder of ecological restoration.
Madany, M.H., and N.E. West. 1983. Livestock grazing—fire regime interactions within montane forests of Zion National Park, Utah. Ecology 64(4):661-667. Ecology of a relict mesa, never grazed by livestock.
Mitchell, J.E. and D.R. Freeman. 1993. Wildlife-livestock-fire interactions on the North Kaibab: A historical review. USDA Forest Service. Gen. Tech. Report RM-222. 12p.
Public Lands Grazing Activist. http://www.grazingactivist.org/ 4/9/03. "Dedicated to reforming the federal government's approach to livestock grazing on lands administered by the U.S.D.A's Forest Service and the U.S.D.I.'s Bureau of Land Management." Includes extensive bibliography.
Savage, M. and Swetnam, T. W. 1990. Early 19th-century fire decline following sheep pasturing in a Navajo ponderosa pine forest. Ecology 71: 2374-2378. Sheep grazing by Navajos reduced fire occurrence as early as 1820 in the Chuska Mountains, AZ.
Southwest Center for Biological Diversity. Livestock grazing, fire regimes, and tree thinning: A bibliographic review. http://www.biologicaldiversity.org/swcbd/Programs/grazing/fire.pdf 4/9/03. Well-researched review of the ecological case against grazing on public lands.
Last edited June 6, 2003